This invention relates to a reciprocating internal combustion engine comprising an engine block, which includes cylinders, cylinder heads, pistons, connecting rods, a crankshaft and the mainshaft bearings for the crankshaft, and which is inserted in an oiltight manner and with the aid of annular supporting elements insulating against a transmission of structure-borne sound in an outer pan, which consists of two parts connected by screws, wherein the engine block is held at its two ends in the outer pan by means of the supporting elements, which are coaxial to the crankshaft and insulate against a transmission of structure-borne sound, and is sealed to the top edge portion of the outer pan only by an oil seal.
Such internal combustion engine is already known from Laid-open German Application No. 28 01 431. In that known engine the annular supporting elements are screw-connected to the two outer crankshaft main bearings, which are obviously included in the engine block. It has now been found that the amplitude of the vertical vibration which is generated in the engine block as a result of the forces which are due to the combustion increases in upward and downward directions from a zone which is disposed approximately midway between the top and bottom dead center positions of the piston heads. That increase is due, inter alia, to the fact that the dimensions of the crankshaft main bearings are necessarily smaller than those of the cylinder block. A particularly large amplitude of vibration occurs in the U-shaped lower parts of the crankshaft main bearings because relatively large deformations of material must be expected in that region. The bending of the crankshaft under the combustion pressure results in a bending of the crankshaft main bearings, which protrude downwardly from the cylinder block, and this results also in a horizontal vibration in the axial direction of the crankshaft. In such an arrangement the supporting elements which insulate against a transmission of structure-borne sound are secured in the very region in which the vertical and horizontal vibrations occurring in the engine block as a result of the forces that are due to the combustion have a large amplitude. A certain improvement in this respect is afforded by the proposal contained in Laid-open German Application No. 28 01 431 to secure the supporting elements only to the upper parts of the crankshaft main bearings. In any case, in view of the large amplitudes of vibration the supporting elements must meet high requirements regarding the preventing of the transmission of said vibrations to the outer pan.
It is already known from Laid-open German Application No. 32 16 318 to provide holders which are secured to the engine block and mount the supporting elements which insulate against a transmission of structure-borne sound. But in accordance with that proposal the holders are secured to the engine block adjacent to the crankshaft and the supporting elements are disposed laterally of the engine block on the outside of the latter.
It is an object of the invention so to improve a reciprocating internal combustion engine of the kind described first hereinbefore that the supporting elements will reliably insulate in any case against a transmission of structure-borne sound.
This object is accomplished in accordance with the invention in that holders for the supporting elements which insulate against a transmission of structure-borne sound are provided and that said holders extend downwardly from the cylinders and are secured to the engine block approximately in the middle of the region between the top and bottom dead center positions of the piston heads.
Because the supporting elements which insulate against a transmission of structure-borne sound are no longer secured to the outer crankshaft main bearings but are provided with separate holders, which are connected to the engine block in a region thereof in which the vertical vibrations generated by the forces that are due to the combustion do not yet have an appreciable amplitude, virtually no vibration of that kind will be transmitted to the supporting elements and a transmission of such vibration to the outer pan is virtually impossible. Similar remarks are applicable to the horizontal vibration because the supporting elements are not in contact with the outer crankshaft main bearings.
A particularly desirable design will be achieved if each holder is channel-shaped and comprises a web engaging the adjacent end face of the engine block and flanges which are screw-connected to the longitudinal side faces of the engine block and each of the supporting elements which insulate against a transmission of structure-borne sound is secured to the web of the associated holder. To ensure an adequate strength of the holders, which preferably consist of sheet metal, stiffening beads may be formed in the flanges of each holder.